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| Wijmstra, T.A.; Hammen, T. van der. |
| A number of pollen diagrams from the Llanos Orientales of Colombia and the Rupununi Savannas of Guyana show that the actual open savannas were preceded by a closed savanna woodland or dry forest with Byrsonima as principal pollen producer. Human influence during the last 3000 years was apparently an important factor in the extension of open savannas. Nevertheless, open savannas occurred also earlier in the Holocene. Even in approximately Late-Glacial time, open savanna sometimes extended temporarily at the expense of the dry forest or woodland. It seems that climatic and atmospheric influences (periods of very dry climate, lightning) were the cause of these extensions. The pollen diagrams suggest anyhow a very unstable equilibrium between the woody... |
| Tipo: Article / Letter to the editor |
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| Ano: 1966 |
URL: http://www.repository.naturalis.nl/record/505833 |
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| Wijmstra, T.A.. |
| In this article the results of a pollen analytical investigation of a section in the tropical lowland of Colombia are discussed. The section has been taken from a lake in the lower course of the River Magdalena (fig. 1). This lake, called ”Cienaga de Morrocayal”, is situated about 20 metres above sea-level; the section represents the greater part of the Subatlantic, and in the course of this period there was a succession of humid and drier periods. These fluctuations seem to represent a cyclic phenomenon. Two C14 analyses of charcoal-samples from the peatlayers, found in this section, showed that these layers were formed at about 1470 A.D. and about 1230 A.D. |
| Tipo: Article / Letter to the editor |
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| Ano: 1967 |
URL: http://www.repository.naturalis.nl/record/505798 |
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